Modern eyeglasses are customarily used to correct the vision of patients or users, with myopia being the most common and prevalent symptom amongst patients. Hereinafter the terms “patient” and “user” are used interchangeably. A main cause of myopia is the inability of the eye's own crystalline lens (hereinafter the “eye lens”) to revert to a lower optical power (or thinner shape) plausibly due to the overly long duration of focusing on near objects which may require a higher optical power (a thicker shape).
When a patient is first diagnosed with myopia, typically at a young age, his or her corrective prescription is often at a relatively low optical power: e.g., −1.5 diopter, which means that the patient can view objects clearly at up to 1/1.5 m=0.667 m=66.7 cm. When the patient, say a student, wears eyeglasses to read a blackboard in a classroom setting, he or she can see the text without much effort. However, when the patient attempts to read a textbook or write notes in a notebook, and the textbook or notebook is at a close distance of 30 cm from the patient's eyes, then utilizing optical equations the virtual image formed by the eyeglasses may be at 1/(−1.5−1/0.3)m=−0.206 m=−20.6 cm. In other words, it is as if the patient is reading or writing at a distance of 20.6 cm instead of 30 cm. Therefore, the patient has to repeatedly change his or her focus between reading/writing and looking at the blackboard, which may be exhausting, and the accommodation (or change of focus) at a near distance may be stronger or greater than if the patient does not wear any eyeglasses. This constant change of focus forces the patient's eye lens(es) into an even higher optical power than before, and after a prolonged period of reading/writing, the eye lens(es) may lose the ability to revert to even the original −1.5 diopter, because during reading/writing the patient effectively focuses at 20.6 cm instead of 66.7 cm, and this may present unhealthy wearing of the eyes. Gradually, a pair of higher prescription eyeglasses would be required by the patient, which may in turn drive the patient's eye lens(es) into unnecessarily high optical powers. Eventually, the mechanical property of the eye lens(es) (which may vary from person to person) may impose a limit on how much the lens(es) may be compressed, thereby stabilizing the user's prescription strength. However, the prescription strength may be stabilized at the great cost of requiring a much higher prescription than the original prescription.
Bifocal, multi-focal and progressive lenses have been used for reading purposes, intended for users with presbyopia (e.g., the inability to focus at near distance when wearing normal prescription eyeglasses, which usually begins to affect vision in middle age). Bifocals, multi-focals and progressive lenses are limited in that they require patients to look down to use the lower prescription part of the lens, which is often inconvenient. Furthermore, eye care professionals seem to believe that these types of lenses are meant for presbyopia patients instead of myopia patients.
PixelOptics, Inc. of Roanoke, Va., has released a type of eyeglasses using adaptive lenses that change focal length depending on viewing distance, however their eyeglasses are intended strictly for presbyopia users and/or older patients, whereas the present disclosure addresses myopia for patients of all ages. Furthermore, the present disclosure is distinguishable from the PixelOptics adaptive lens in that given a prescription that the patient has no problem using to view objects at close distance, the focal length is adapted accordingly, whereas the PixelOptics eyeglasses are not known to perform such adaptation. Furthermore, the PixelOptics eyeglasses vaguely perform eye tracking, but not the specific eye tracking as disclosed by the present disclosure. U.S. Pat. No. 7,517,083, assigned to PixelOptics, potentially suggests the use of eye or gaze tracking to control the focal length of adaptive lens. However, the patent does not provide sufficient detail on implementing eye tracking, and merely mentions the use of LEDs and image sensors for detecting the edges of pupils, which suggests pupil-based eye tracking, but no details are provided to implement pupil tracking with a small form factor and in addition, inter-pupillary distances are suggested in the patent for determining viewing distance. However, the inter-pupillary distances are not completely accurate when a patient looks sideways whereas using a “line-of-sight” intersection approach to calculate the distance is generally more accurate. Furthermore, the concept of inter-pupillary distance tacitly assumes that there is one gaze distance from both eyes, but that is true only when the user looks straight ahead (e.g., up or down is acceptable). For instance, when looking to the left side, especially for close objects, the left eye will be closer to that object than the right eye. The line-of-sight intersection approach does not encounter this problem.
A range finder method is also discussed in U.S. Pat. No. 7,517,083, which generally finds the closest straight-ahead object, which is not the same as finding the gaze distance. According to various PixelOptics literature and press releases, its newly released eyeglasses may be capable of “knowing where you're looking at.”
Furthermore, U.S. Pat. No. 7,517,083 mentions using a tracking system to “calculate the range of near point focus in order to correct for one's accommodative and convergence near or intermediate range focusing needs”, which is a vague description that seems to apply strictly to the focusing needs of presbyopia users and not the focusing needs of myopia users.
In addition, the type of eye tracking discussed in U.S. Pat. No. 7,517,083 are most often utilized for correcting non-conventional aberrations in vision such as, for example, astigmatism, instead of more commonly occurring aberrations such as, for example, myopia. In practice, eye or gaze tracking is complex and is a concept that should be discussed in clearer and fuller detail, especially in a small form factor context.
Eye or gaze tracking itself is a complicated subject that has been around for decades and still is non-trivial to implement. The technology surrounding eye or gaze tracking has advanced significantly, enabling optical manufacturers to spend large amounts of money to make and produce commercial trackers (or Head-Mounted Eye Trackers), which may be sold for upwards of thousands of dollars. Existing research suggests that Head-Mounted Eye trackers are relatively bulky and consume significant amounts of energy, perhaps hundreds of mW (milli-Watts).
One 2009 paper, entitled “A 200 μs Processing Time Smart Image Sensor for an Eye Tracker Using Pixel-Level Analog Image Processing” describes a Smart CMOS image sensor that directly implements eye tracking at a 100 mW peak consumption. See Dongsoo Kim, Gunhee Han (Dept. of Electrical Engineering, Yonsei University, Seoul, Korea), A 200 μs Processing Time Smart Image Sensor for an Eye Tracker Using Pixel-Level Analog Image Processing, 44 IEEE JOURNAL OF SOLID-STATE CIRCUITS 2581-90 (September 2009) (Volume 44, Issue 9). The paper discusses the current state-of-the-art of low-power design for eye trackers and shows how attempting to develop a sub-mW consumption remains a key design goal. However, the paper does not achieve sub-mW consumption. The design discussed in the above paper supports 5000 trackings per second. Thus, if the number of trackings were reduced to just 50 trackings per second, then the total power consumption may be able to be reduced to 1 mW.
One 2004 paper, entitled “Ambient-Light-Canceling Camera Using Subtraction of Frames”, proposes double exposures with time modulated (On/Off) controlled lighting and then subtraction to cancel ambient (background) light interference. See NASA's Jet Propulsion Laboratory (Pasadena, Calif.), Ambient-Light-Canceling Camera Using Subtraction of Frames, NASA TECH BRIEFS, NPO-30875 (May 2004), available at: http://findarticles.com/p/articles/mi_qa3957/is_200405/ai_n9457885/?tag=content;col1. The subtraction may be done in software instead of hardware.
In addition, U.S. Patent Publication No. 2008/0203277 by Zamir Recognition Systems, a company located in both Knoxville, Tenn. and Jerusalem, Israel, describes an approach similar to the above-mentioned approach of the above-mentioned 2004 NASA Tech Brief, but in hardware. Two approaches are outlined in the above-mentioned Patent Publication: (i) one approach using a time modulated (On/Off) controlled light like in the above-mentioned 2004 NASA Tech Brief and (ii) the other approach using frequency modulation (similar to AM/FM radio tuning) to be more receptive to certain controlled frequencies. The frequency modulation approach may be more complex to implement compared to the time modulated approach. Each pixel in the camera has a capacitor. The time-modulated approach may use charging and discharging the capacitor of each pixel in one array of pixels, or charging two arrays of pixels, and then performing subtraction.
FIG. 3 of U.S. Patent Publication No. 2008/0203277 seems to exhibit a static electricity hazard, which is logically inconsistent with the overall design of a charging and discharging approach. Furthermore, for the time-modulation approach with two pixel arrays, the subtraction of signals in hardware or software is suggested. Even for hardware subtraction, U.S. Patent Publication No. 2008/0203277 appears to suggest that prior art methods are used, e.g., a differential operational amplifier is typically used as a subtraction module in the analog domain, and an arithmetic unit after digitization is typically used as a subtraction module in the digital domain.